The renegade Maverick who pilots a Ride Armor in Mega Man X is Vile. He is a former Maverick Hunter who joins Sigma and becomes one of the game’s major antagonists, fighting X and Zero during the opening conflict.
Vile is built around heavy firepower and mobility rather than simply copying X’s abilities. His Ride Armor gives him a large mechanical combat platform with powerful weapons, allowing him to smash through obstacles and overpower ordinary enemies. In the opening stage, X confronts Vile but cannot defeat him because Vile’s armor and weaponry are too strong; Zero intervenes and helps X survive.
Vile’s name is used in English releases, while he is known as VAVA in Japan. That difference can create confusion when comparing Japanese manuals, games, and reference material. He is also sometimes described as a Maverick, although his earlier service with the Maverick Hunters is an important part of his backstory.
The answer is not Armored Armadillo, Chill Penguin, or Spark Mandrill. Those three are stage bosses in Mega Man X, while Vile is the recurring rival and antagonist associated with the Ride Armor encounter.